Spark plug



L. J. TETLOW SPARK PLUG Filed July 24. 1931 May 28, 1935.

Patented May 28, 1935 UNITED STATES PATENT OFFICE 22 Claims.

This invention relates to spark plugs of multiple telescoping insulator construction and has for its object the provision of a spark plug of exceptional sturdiness in which provision has been made to assure against a loss of spark even tho one or more of the telescoping insulating sleeves should crack.

Further objects of the present invention relate to specic details such, for example, as the provision of mica washers between the two insulator pieces which make up the body of the plug.

Other objects of the invention will be apparent from study-of the claims and from the accompanying drawing which illustrates forms that the invention may take.

In the drawing:

Figure 1 is an elevation.

Figure 2 is a central section.

Figure 3 is a bottom plan view.

Figure 4 is a somewhat modified form.

Figure 5 is a detail showing a modication of one of the spark plug elements.

In the form of device illustrated in Figure l, the shell I0 is of ordinary and well known form having an integral nut I I at the top and a threaded portion I2 to lit into the cylinder of an engine. A slight variation from ordinary practice is the provision at the bottom of the shell oi a disk I4 having a knurled periphery I5 and having two bisecting slots I6 forming a cross, the cusps Il of which are the sparking points. The central electrode I8 should be so positioned that it is equi-distant from all four of the cusps.

The body of the plug consists of four major portions, a top insulator section 20, a nut or bushing 2l surrounding the top section, a lower insulator section or core 22 and cap 23. The latter consists of a threaded terminal 24 integral with 40 the cup portion which, when the device is assembled, is spun so that its peripheral portion 25 snugly and permanently engages the groove 26 in the upper insulator section 20. In the form shown in Figure 2 the central electrode I8 is driven into a small hole in the cup and is held to the cup by such engagement prior to assembly of the various parts of the plug.

The top insulator section has a cylindrical top portion 21 snugly fitting the cap 23, a mid portion which is the frustum of an ellipsoid 28, and a lower cylindrical portion 29 which nts snug ly the central bore of the bushing or nut 2 I.

Thru the center of the upper insulating body are three coaxial bores, the lower boreV 30 being fairly large and intended to receive the core (Cl. 12B-169) section, the upper portion of the bore 3I being somewhat smaller and of a size to receive a collar 32 which is shrunk on a central electrode I8, while the intermediate bore section 34 is just of size to receive well the central electrode. By reason of the three bores two annular shoulders are formed, the upper one to receive an additional collar 32 when desired and the lower annular shoulder to abut the upper cylindrical surface of the core which however is not intended to abut rmly against the shoulder.

The core 22 consists of an upper cylindrical section 3l and a lower conical section 38, these two being integral and joined by an appreciable iillet 39 to prevent the formation of a sharp angle between the two integral sections. Between the wall of the larger bore in the upper insulating section and the appreciably smaller cylindrical wall of the top section 3l of the core I place a cylinder of mica preferably in spiral form. This mica, when the spark plug is nished, is securely held to both the inside of the upper insulating section 2U and the outside of the lower insulating section or core, the latter preferably having a number of annular grooves 40 to aid in the holding of the cementing material, the annular grooves 4I in the cylindrical lower portion of the section 20 being for the same purpose and cooperatinglwith a roughened surface of the nut.

A steel disk 43 is force fitted into the bottom of the nut, this construction being much more 'satisfactory in practice than the obvious equivalent of making thevwasher and nut integral. Between the washer 43 and the surface at the top of the cone 38 I apply a number of annular mica disks 44 which cushion the core 22 against the nut or bushing 2| and also against the inner section 20 should the washer not be used. While the central electrode I8 ts the core as snugly as is possible in practice throughout the upper section of the core I desire that the size of the opening to receive the central electrode shall be appreciably larger thru the 'conical section as is indicated at 45, this permitting the rather necessary movement of the lower end of the electrode.

In assembling the device I drive the central electrode into the cup and then apply the terminal nut 4E, placing the one or more collars 32 at desired positions along the rod I8. The sleeve of mica or other tough non-cracking insulating material which, while preferably in the form of a roll made of an integral sheet, can consist of a number of different sheets, is secured to the upper section 20 and packed in place, the nut 2I likewise being secured in the same manner and preferably at the same time. After applying the mica washers id I next insert the core into position threading it on the central electrode i8 should that be placed into position rst. Preferably, however, I apply the electrode and cap after the body of the plug has been completely secured together as in this way I am able to secure a better distribution of the cementing material, using the collar 32 as 'a piston to force the cement into the bore below this collar. It is to be noted that the actual joint between the nut and the body portion 2Q is at i? so that thereis Y no pressure on the washer i3 and it is also to be noted that the joint between the two porcelain sections is at the top of the cone 3S and 4not at the top of the cylindrical portion "3?. Due to the construction set forth I amable to-sccure'great l advantages as I can make the upper section 2G of a grade of porcelain much better able to with- "stand 4the 4 rough treatment that thisportion will ,be 'subjected to A*.andI can also make the lower section of, material ywhich will stand much .greateriheat Ordinarily the composition of the porcelain imust b e ea compromise between rine- :ness :and ,ability to withstand heat and tough'- ncss and ability to withstand blows but by using vthetwo ,telescoping sections I am able to `secure the maximum advantage of each of these parts without any sacrifice whatsoever. Furthermore because ofthe provision of the relatively heavy mica sleeve :36 I secure .a much greater klife as the;mica sleeve located between the inner heat resisting vsection and .the outer `tor-.gher section -olcviatcs :any p ossibility of loss of current because :of the Vcracking iof .either of the Vouter or inner porcelain sections or both.

In the :modied ,form shown in Figure 4 the I-cap i5@ -is'threaded'.to the upperporcelain section l :and ,carries gazrnercury cup d2 ,into which the 4central'electrode153 penetrates. On ,this central Yelectrode near .itstop areltwo spaced collars 'and gfthelatter engagingsnugly the upper .face ofthe cylindrical portion 5l' of .the core Eil and Y,the :formerfholding va micawasher ,5.9 against Athe Ydownwardlyturned opcnend'cf the vmercury cup f5.2. :Either or vboth vof Athese vcollars may be pmitted but I prefer to use the two of them. 'Iheymay bemadeeither of brass or copperand may be held to the electrode V.in any `desired .-manner. .My ,preference ,fis to shrink these Acollars tothe electrode with a reasonable tightness Abut not .so great .as 4.to prevent 1a desired Vshifting of the collars Ashould it be necessary. In this modified :form Iplace va series of washers S3 between the upper `sectionof Vthe body and thebushing V2l. The shell lis the same as in Figure 1 butinsteadof having the lower plate l I use the :more conventional :horizontal electrodes lili .radially :disposed in lthe shell at V120 :apart and `triade `'slightly adjustable for accurate spacing. In this 4form of plug I prefer that the copper vgasket 1&5, whichforms-a gas tightjoint between the couplernut or bushing and the shell, shall be .stLdicientlyrsmall as ,not torengage the washer G3.

WhatI claim is: Y

, 1. A spark plug insulator comprising an inner core fof iceramic material having fhigh Yhe at resistance, :an outer shell of ceramic material having .ihigh resistance to breakage, vand a mica tube betweenthe shell andthe core, the grain jof the amica :being parallel lwith the vsurface or" `the zcore. 2. AAfspark pluginsulator consistingof an inner core, .anonter fbodyfportion Aof insulating material, and a 'sleeve :of .iibrous .material such as mica between the core and body portion said sleeve having high tensile strength.

3. In a spark plug, an insulator having a connector cap supporting end and a shell engaging end, a relatively large bore in said insulator divided near the cap end by a partition having a small central bore connecting said large bores, a shouldered tube of insulation extending within said larger bore at the shell engaging end, a metal washer surrounding the tube and engaging said shoulder and having an outer diameter greater than that of the shell engaging end, said washer .separating the said shell engaging end and saidv shoulder.

4. The device of claim 3 in which the tube and insulatorareseparated by a mica sleeve extending rom said washer to said partition.

i5. ,Ina spark plug an insulator body having a head, acentral electrode and a cap, a bore in said head, a washer in said bore in force t engagef ment withsaid electrode, said capV having a `centralV bore in which said electrode is in force .t engagement, vand said cap being spun on vsaid Yhead whereby when fully assembled the length of electrode between the washer and cap is under compression.

6. In a spark plug, a main insulator body havingra relatively large bore extending from thev bottom toward the top, a tube of mica fitted in the bore, a second .insulator body fitting in'said l` mica tube, an integral shoulder on the lower end oi said second body, a washer between said shoulder and thelower end oi'said main bodyand extending, beyond said body formingfan annular ledge for engaging the lshell of the plug, an elecf 8. A spark plug rinsulator consisting of a `central core having a cylindrical portionanclaisubstantially conical portion, 'an insulator 4sleeve entirely surrounding the cylindrical vportion of the core, a bushing permanently 'secured ftozth'e sleeve, an electrode thru the core, a .cap 'onthe sleeve and in electric contact withthe electrode, and a collar on the electrode spaced .from the cap and 'within said sleeve.

9. A core for a spark plug consisting of `a conical section adapted -to be spaced within the bore of the electrode carrying shell and an Aintegral cylindrical section, said cylindrical section and said conical section being vjoinedby an annular fillet and said cylindrical section `having an annular groove in its -outer surface whereby iit -may be cemented to a supporting-elementsurrounding 'said cylindrical section.

l0. A spark plug having a central electrode, an

Vinsulating member of Vceramic vmaterial "surrounding'a portion of the electrode, a'niicafsleeve surrounding Va portion 'of :said tinem'ber `and an insulating jacket of ceramic imaterial 'surrounding said `mica sleeve.

11. Ina spark plug insulator, a central electrode, an insulating :sleeve surrounding the greater portion of the electrode, asecondlinsulating sleeve surrounding the' greater .portion of said rst sleeve, and aniinsulating tube .of mica or the like .between said sleeves. Y

12. In a spark plug insulator, a Vbody of itwo sections, one a core and the other an outer and top section, said core being supported by said outer section, a metal bushing carrying the top section to secure it to a shell, said bushing having an abutment to engage the core to prevent transfer of pressure from the core to the top section.

13. In a spark plug having a shell, a baiiie plate held in place by a turned over edge of said shell, said edge being knurled.

14. In a spark plug, a shell, a core mounted in the shell and spaced therefrom, a metal bushing having threaded engagement with the shell, means carried by the bushing to engage the core to prevent the core from moving away from the shell and insulating means for shielding the upper portion of the core, said insulating means having a curved surface of downwardly increasing radius to deilect dust and dirt from the core and terminal means carried by said deflecting means.

l5. In combination, a shell having an inwardly directed electrode, a bushing having threaded engagement with said shell, a core having a cylindrical sleeve portion within the bushing and having an enlarged portion tting against the bushing whereby the enlarged portion of the core is suspended between the bushing and the inwardly directed electrode, a sleeve of insulating material surrounding the cylindrical sleeve portion of the core and resting on a portion of the bushing and a second insulating sleeve surrounding said iirst insulating sleeve and being permanently attached to the bushing but out of contact with the enlarged portion of the core-` said core being supported by said iirst insulating sleeve.

16. In a spark plug insulator, a bushing adapted to be secured to a shell, a top insulator section permanently secured to the bushing and having an extended portion rmly seated on the top oi the bushing, a core section of the insulating body telescoping Within the top section of the body, an annular washer seated in the bushing below the top section of the body, an enlarged portion on the core below said washer, and yielding insulating disks between said enlarged portion and said washer.

l. In a spark plug insulator, the combination with a bushing having a bore of diameter to receive a body member, said bushing also having a restricted bore communicating with the first mentioned bore and of size to receive a core, a core of insulating material having a cylindrical portion of a size to fit snugly within the smaller bore of the bushing and having a head below said smaller bore, and a plurality of insulating yielding disks surrounding the cylindrical portion of the core and being held in place against the lower face of the bushing by the enlarged portion of the core.

18. In a spark plug, a shell carrying a ground electrode, an insulating member carrying a central electrode, a bushing having a threaded engagement with the shell and with the insulator, and a cap having a threaded engagement with the insulator and adapted to be placed in electrical communication with the central electrode.

19. In a spark plug, a bushing, an outer porcelain body permanently secured to said bushing, a porcelain core extending into said body and separated therefrom by a cushioning tube of mica, said body, core and bushing being cemented together to form a unit, and a shell for receiving said unit by means of threaded engagement with said bushing, said core being free of said shell when the bushing is screwed therein.

20. A spark plug consisting of a central core having a cylindrical portion and a conical portion, an insulator sleeve entirely surrounding the cylindrical portion of the core, a bushing secured to the sleeve, and an electrode thru the core, said electrode being free of the core where it passes thru said conical portion whereby contraction i and expansion of the electrode puts stresses only on the cylindrical portion of said core.

The device of claim having a shell in threaded engagement with said bushing, an internal shoulder on said shell, a gasket between said shoulder and the base of said bushing, said sleeve and said core being entirely separated from said shell and said gasket whereby compression of said gasket between the shell and bushing puts strain only on the sleeve and cylindrical portion.

22, In a spark plug, a main insulator body having a relatively large bore extending from the bottom to a point just above the center, a tube of mica fitted in the bore, a second insulator body fitting in said mica tube, an integral shoulder on the lower end of said second body, a washer between said shoulder and the lower end of said main body and extending beyond said body forming an annular ledge for engaging the shell of the plug, an electrode thru the center of said bodies and carried thereby.

LEWIS J. TETLOW. 

